Alzheimer's disease is the most common form of dementia in older people. As a result of population aging worldwide, the prevalence of this disease is set to increase significantly in coming years. As such, there is an urgent need to develop better prognostic and diagnostic tools and new treatments for people identified as having this disease.
Alzheimer's disease is a chronic neurodegenerative disorder characterised by selective loss of cortical neurons within the hippocampus and the temporal and frontal lobes of the brain. The neurodegenerative process occurring in Alzheimer's disease is accompanied by progressive cognitive impairment leading ultimately to dementia in affected individuals.
There is currently no accepted “gold standard” diagnostic test for Alzheimer's disease in the live patient. This reflects the difficulties associated with identifying patients who would go on to be classified as having this disease at post mortem examination. Clinical diagnosis of Alzheimer's disease is typically based on evaluation of clinical criteria, such as the NINCDS/ADRDA criteria (McKhann, G. et al., (1984) Neurology 34: 939-944).
The problem with the diagnostic methods used to date lies in the fact that patients are typically diagnosed once clinical dementia has started to develop. It follows therefore, that existing treatment strategies are limited to agents used primarily to manage the symptoms of disease. For example, cholinesterase inhibitors are administered to patients so as to block the degradation of the neurotransmitter acetylcholine and thereby enhance neurotransmission in the brain. Use of such agents can help to preserve cognitive function, but does not improve the underlying pathology and is therefore not a curative approach.
Although the etiology of Alzheimer's disease is poorly understood, the neuropathology associated with the development of this disease has been relatively well characterised. The classical hallmarks of this disease consist of amyloid-β plaques, which accumulate in the brain, and neurofibrillary tangles (NFT) consisting of hyperphosphorylated tau protein present in affected neurons. Additional changes occurring at the cellular level, which are now thought to precede the deposition of plaques and NFTs, include damage to cells caused by oxidative stress, mitochondrial malfunction and aberrant re-entry of neurons into the cell division cycle.
In addition to difficulties associated with diagnosing Alzheimer's disease, there are also problems associated with identifying individuals in the population who are at increased and/or decreased risk of developing Alzheimer's disease during their lifetime, as compared with the average level of risk associated with the general population. The only known genetic risk factor for late onset sporadic form of Alzheimer's disease is the polymorphism on the ApoE gene. Other discovered polymorphisms appear to be restricted to relatively small patient subgroups. Thus risk prediction or assessment of susceptibility, before the development of clinical Alzheimer's disease, is difficult as well.
There is now good evidence to suggest that the neuropathology underlying Alzheimer's disease begins years, maybe even a decade, prior to the diagnosis of clinical dementia (Forlenza et al., (2010) BMC Medicine 8:89). Based on these observations, the continuum of Alzheimer's disease progression has been classified into three phases:    (i) asymptomatic Alzheimer's disease (preclinical stage);    (ii) mild cognitive impairment (MCI) due to Alzheimer's disease (pre-dementia stage); and    (iii) clinically-defined Alzheimer's disease (dementia).
In light of the above, there now exist several opportunities for improved management of Alzheimer's disease. In particular, it may be possible to identify individuals at increased risk of developing Alzheimer's disease, and/or diagnose individuals at a much earlier stage of disease, for example, individuals with asymptomatic disease or those patients with MCI that will go on to develop clinically-defined Alzheimer's disease. If susceptible individuals can be identified and/or diagnosed at an earlier stage of disease, it will be possible to develop, test and use new preventative and/or curative treatments intended to stabilize and/or reverse the neurodegenerative process and thereby prevent cognitive decline.
Researchers are already using the improved knowledge of Alzheimer's disease pathogenesis to develop more effective methods of diagnosis and treatment. In this regard, diagnostic biomarkers have been identified that can be measured in humoral fluids, mainly cerebrospinal fluids, and biomarkers that may be detected using advanced neuroimaging methods (Gustaw-Rothenberg et al., (2010) Biomark. Med. 4(1):15-26).
Furthermore, new “disease-modifying” treatments are being developed that tackle the deposition of β-amyloid plaques and NFTs (Bonda et al., (2010) Curr. Opin. Drug Discov Devel. 13(2): 235-246)
There remains however, an ongoing need to improve methods for the diagnosis and treatment of Alzheimer's disease, particularly early-stages of disease. The present invention seeks to address these issues.